1. Field of the Invention
The present invention relates generally to a safety mechanism. More particularly the present invention relates to a safety release device for providing adequate ventilation for a livestock confinement operation in the event of a sustained power loss.
2. Background Art
Livestock raising operations are often confinement operations, today. Large numbers of livestock are housed inside a building with artificial lighting and ventilation. Because the livestock must have ventilation to survive, when electrical power fails for more than a few minutes, special measures must be taken to ensure that ventilation.
Ventilation is provided by fans, in normal circumstances, with heavy curtains over openings in the confinement building walls to provide a path for air to enter the confinement space. The amount of opening of the curtains is normally dictated by the building temperature and fresh air requirements. Opening and closing the heavy (2000-4000 lb.) curtains is accomplished by a screw actuator connected to a cable. Manual operation is also possible via a hand crank.
When the utility grid goes down, the usual action is to release the manual hand crank after a brief delay. The crank, after being released, will spin due to the weight of the curtains. The curtains are open providing ventilation when they are lowered.
A device for releasing the manual crank for ventilation curtains in a livestock confinement operation was disclosed by Sutton in U.S. Pat. No. 5,325,813. The device is mounted at the crank handle and cradles the handle in a hook. The hook is held in the xe2x80x9choldxe2x80x9d position by an electromagnet. When power is interrupted to the electromagnet, the hook is released which releases the crank and permits the curtains to drop. The release system is not contained in a single unit. The electrical box to which the electromagnet is wired is separate from the hook and electromagnet unit.
In U.S. Pat. No. 4,428,278, Sutton discloses a different livestock curtain release device. This one is also held in the xe2x80x9choldxe2x80x9d position by an electromagnet, but the handle of the manual crank is connected to the release device via a rope. The release device must be carefully mounted at an angle providing secure holding, but also resulting in a proper release when the power is interrupted. This device will not usually release the rope if there is no tension in the rope due to frozen curtains or a rusty mechanism.
A delay, so the release mechanism can sustain very brief power interruptions, is provided by capacitors. This system is, again, not contained in a single unit.
A commonly used curtain safety release device is disclosed in U.S. Pat. No. 4,605,162. This device uses a U-shaped xe2x80x9cexpansion fingerxe2x80x9d inserted in a sleeve. The sleeve is heated (using resistance heat) and the expansion finger expands due to the higher temperature. This provides the security for holding the manual curtain crank and also the delay for tolerating very brief power outages. The sleeve and expansion finger represent significant thermal mass, which take some time to cool down when the resistance heat is interrupted. The manual curtain crank is held by a lever. The lever is held by a cord or cable operably attached to the expansion finger. When the sleeve cools, the cord is released and the lever arm pivots out of the way so the crank will release.
The U-shaped expansion finger is bent to the required shape by an operatorxe2x80x94introducing a possible error in the system. When first engaging the curtain release system, the operator must hold the device until it is adequately heated to secure the crank in the xe2x80x9choldxe2x80x9d position. This may take several minutes.
This curtain release device will not function if there is no tension in the cord. Again, if the curtains are frozen or the crank mechanism is slightly rusty, the release action may fail. Also, conditions that enhance heat transfer from the sleeve such as a cold rain can cause this device to fail.
A simple electromagnetic device with a battery backup is disclosed in U.S. Pat. No. 5,924,924. This invention is a short chain, anchored to a wall at one end and connected to an electromagnet at the other. An armature is operably connected to the manual curtain crank, and is magnetically attached to the electromagnet when the electromagnet is energized. When the electromagnet is not energized, the armature drops off and the crank is free to rotate and let the ventilation curtains drop.
The unit is backed up by a battery to provide a delay for when the utility grid is interrupted for only a brief time. A timer provides the actual duration of delay. If the timing circuit fails for any reason, the battery has the capacity to maintain energy to the electromagnet well beyond the point at which the livestock begin to suffer due to lack of ventilation.
There is, therefore, a need for a method and device for automatically and reliably permitting the opening of the ventilation curtains in a livestock confinement building. There is a further need for a ventilation curtain release system that is contained in a single unit.
A purpose of this invention is to provide a simple, reliable method and apparatus for releasing ventilation curtains in a livestock confinement building when the power to the forced ventilation system fails for more than a brief time. Such confinement buildings include, but are not limited to, poultry houses and hog confinement buildings.
A screw actuator is modulated by a control system to vary the opening of the ventilation curtains based on the needs of the livestock inside. A hand-crank is provided for manually carrying out the same operation. If the hand-crank is released, the weight of the ventilation curtains will cause the crank to spin, allowing the ventilation curtains to open.
If utility grid power is interrupted, the preferred failed-mode of the curtains is 100% open, to assure adequate ventilation is provided to the livestock in the building. To effect this 100% opening without power, the manual hand-crank is automatically released.
A safety ventilation curtain release device comprises a hinged plate with an integral hook, an electromagnet and either two permanent magnets or a spring. The hinged plate is maintained in a desired position by the electromagnet. The hook engages one end of a tension device, which would be a device such as a cord, chain, cable, string or wire. The other end of the tension device is attached to the manual hand-crank. In one embodiment of the invention, two permanent magnets are mounted with like poles adjacent to one another, one permanent magnet on the hinged plate, the other on a stationary plate. In a second embodiment, a spring replaces the permanent magnets. When the utility grid is interrupted, capacitors provide power to the electromagnet for a known period of time. Once the capacitors have discharged sufficiently, the electromagnet releases the hinged plate. The permanent magnets in the first embodiment, or the spring in the second embodiment provide a force to the hinged plate to ensure it will pivot away from the electromagnet and release the tension device.
The safety ventilation curtain release device is powered using the same 240 volt circuit the ventilation fans utilize. If either or both legs of the power are interrupted, the capacitors will continue to energize the electromagnet for a predetermined time span from the instant power is lost. When the capacitors have discharged, the electromagnet is deenergized, causing the curtains to drop, unless electrical power is restored before the capacitors have deenergized.
The capacitors used in the safety ventilation curtain release device are supercapacitors providing a total capacitance on the order of 100 Farads.
The safety ventilation curtain release device is packaged in a single unit, requiring only to be plugged into the same circuit as that of the ventilation fans, and affixed to a stationary surface somewhat near the manual curtain hand-crank.
The novel features which are believed to be characteristic of this invention, both as to its organization and method operation together with further objectives and advantages thereto, will be better understood from the following description considered in connection with accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood however, that the drawings are for the purpose of illustration and description only and not intended as a definition of the limits of the invention.